otherwise there is a z-distance between the sphere defining which photons are written to the output file and the telescope position. For inclined photons this leads to photons recorded far away from the telescope position.

Now, call coconut

[1] cd corsika-76400
[2] ./coconut

You can use the defaults (just press return) for

Compile in 32 or 64bit mode? [64 bit]

Which high energy hadronic interaction model do you want to use? [QGSJET 01C]

Which low energy hadronic interaction model do you want to use? [GHEISHA 2002d]

Options description

IACT[1b]: Redirects photons to eventio (telescope.dat) file (CER files exists, but only for one telescope and it is empty), extends wavelength range to 2000nm.

CERWLEN: Calculates a wavelength dependent refractive index for each step and replaces the production height (8-th) in the photon output by the wavelength.

IACTEXT: Write also particles to eventio file

CEFFIC[1c]: All three look-up-tables (QE, Atmabs, Mirror) are limited to 105 values between 180nm and 700nm -> This turns the extension to 2000nm in the IACT option off

TRAJECT[1e]: To be able to simulate along a trajetory (zd, az, orientation to magnetic field) with "TRAFLG T" (Turn off with "TRAFLG F")

THIN[2a]: Thinning is mainly interesting for >PeV showers and calculates average results for high densities. With CEFFIC and/or CERWLEN, the wavelength is written 8th value to the Cherenkov bunch into the CER-file instead of the weight. To turn the thinning off for the production use "THIN 0 1 0" (The production should behave like with no THIN option). To turn thinning only off for electromagnetic-particles use "THINEM 0 1"

VIEWCONE[7c]: Logically allows to simulate a cone rather than a rectangle in Alt/Az

ATMEXT[9]: To use an atmosphere from an input file rather than a built-in atmosphere

This is from the tracking of the electrons through the Earth's magnetic field

For me this seems only relevant if someone wants to backtrack a single muon, i.e. determin its arrival direction.

An interesting possibility of the IACT option is:

j) Starting with version 1.25, the package has been prepared for importance sampling ofcore position offsets. This would mean that actual core offsets can be generated in anon-uniform distribution and can extend to different distances, depending on primaryenergy, primary type, zenith angle and so on. This package, however, does not provide areal implementation of importance sampling (other than for testing that the later stagesof the processing properly get the weights for each event). If you do nothing about it,you will get uniformly distributed core offsets as before. If you plan to make use ofimportance sampling, you have to replace the file ’sampling.c’ with an implementationof your choice.

A problem with the IACT option might be this:

m) Starting with version 1.38, the dynamic range in a telescope is basically unlimited dueto automatic thinning of bunches. When a detector sphere is hit by more than the givenmaximum number of bunches, the actual number of bunches is reduced by increasingpowers of two, by discarding every second bunch and increasing the bunch size of theremaining bunches by factors of two. Very large eventio buffers are now possible on64-bit machines. They were formerly limited to less than 1 GiB per telescope array andevent and now to 2 GiB on 32-bit machines but can be increased to 4 Terabytes on 64-bitmachines.

The secret of wavelength 999 and 9999 in eventio:

IACTEXT The interface to theTELOUTfunction is extended by parameters describing theemitting particle. This extended information is stored as an additional photon bunch(after the normal one) with mass, charge, energy, and emission time replacing thecx,cy,photons, andzemfields, respectively, and are identified by a wavelength of 9999.The compact output format is disabled for making that possible. In addition, all particlesarriving at the CORSIKA observation level are included in the eventio format output file,in a photon-bunch like block identified by array and detector numbers 999.

MMCS

The current version of MARS is NOT compatible anymore with MMCS output. Although the code is still there and can be enables, it is turned off by default (see MPhotonData.cc)

Conclusion

If we want to do any absorption in Corsika (CEFFIC), we have to patch Corsika to allow wavelength larger than 700nm or accept that we will miss photons above 700nm.

To be able to define telescope positions ("TELESCOPE"), the IACT option is not required. Plain Corsika can nowadays do that.

Enabling IACT might make sense, due to the code snippets shown above, the automatic thinning (faster) and the work on improving runtime by faster interpolation algorithms.

The disadvantage of the IACT option is that teh data of all telescopes end up in the same file and that *eventio* format has to be used. Although, the iACT options writes a temporary file for each individual telescope, they are sorted together into one file later.

Using IACT means that we have to understand the automatic thinning and implement it and to make sure eventio works.

I have the impression that eventio files are larger than the corsika output (which is a bit strange)... this has to be checked with long runs and high statistics!

Examples

Here is an example input card for gammas (not all options have yet reasonable values!)